Liquid crystal display apparatus having improved gray scale display characteristics

ABSTRACT

In a liquid crystal display apparatus including two electrodes and a twisted-mode type liquid crystal layer inserted between the electrodes, an electric field in the liquid crystal layer between the electrodes is changed within one pixel, when a voltage is applied between the electrodes.

This application is a division of Ser. No. 09/347,237 filed Jul. 2,1999, now U.S. Pat. No. 6,160,602, which is a divisional of Ser. No.08/840,389 filed Apr. 29, 1997, now U.S. Pat. No. 6,008,875.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a twisted nematic (TN)-mode liquidcrystal display (LCD) apparatus capable of improving gray scale displaycharacteristics.

2. Description of the Related Art

In a prior art TN-mode LCD apparatus, twisted-mode type liquid crystalis inserted between two plane electrodes. In the prior art LCDapparatus, when the twisted angle of liquid-crystal molecules in theliquid crystal is larger than a value around 270′, the tilt angle ofliquid crystal molecules has an S shaped relationship to the voltageapplied between the electrodes. Therefore, the transient orientationstate of liquid crystal molecules during a rising voltage is differentfrom that during a falling voltage. As a result, when an intermediatevoltage between a high voltage and a low voltage is applied between theelectrodes there are two orientation states of liquid crystal moleculesmixed within one pixel. Thus, a large hysteresis is generated in thevoltage-to-light transmittance characteristics, so that a gray scaledisplay is impossible.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a TN-mode LCDapparatus capable of improving gray scale display characteristics evenwhen the twisted angle of liquid crystal molecules is large.

According to the present invention, in a liquid crystal displayapparatus including two electrodes and a twisted-mode type liquidcrystal layer inserted between the electrodes, an electric field in theliquid crystal layer between the first and second electrodes is changedwithin one pixel, when a voltage is applied between the electrodes.

Also, in a liquid crystal display apparatus including two electrodes,two oriented layers formed on inner surfaces of the electrodes,respectively, and a twisted-mode type liquid crystal layer insertedbetween the oriented layers, one of the electrodes has an unevensurface, so that pretilt angles of liquid crystal molecules in theliquid crystal layer are fluctuated within one pixel.

Further, in a liquid crystal display apparatus including two planeelectrodes, two oriented layers formed on inner surfaces of theelectrodes, respectively, and a twisted-mode type liquid crystal layerinserted between the oriented layers, one of the oriented layers isdivided into a plurality of domains each receiving rubbing processes ofdifferent directions, so that pretilt angles of liquid crystal moleculesin the liquid crystal layer are fluctuated within one pixel.

In addition, in a liquid crystal display apparatus including two planeelectrodes, two oriented layers formed on inner surfaces of theelectrodes, respectively, and a twisted-mode type liquid crystal layerinserted between the oriented layers, the liquid crystal layer includesa polymer network generated by polymerization of monomer, so thatpretilt angles of liquid crystal molecules in the liquid crystal layerare fluctuated within one pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below, as compared with the prior art, withreference to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view illustrating a prior arttransmission-type TN-mode LCD apparatus;

FIG. 2 is a photograph showing an orientation defect in the liquidcrystal layer of FIG. 1;

FIG. 3 is a graph showing the voltage-to-light transmittancecharacteristics of the liquid crystal layer of FIG. 1;

FIG. 4 is a cross-sectional view illustrating a first embodiment of theTN-mode LCD apparatus according to the present invention;

FIG. 5 is a graph showing the voltage-to-light transmittancecharacteristics of the liquid crystal layer of FIG. 4;

FIG. 6 is a cross-sectional view illustrating a second embodiment of theTN-mode LCD apparatus according to the present invention;

FIG. 7 is a cross-sectional view illustrating a third embodiment of theTN-mode LCD apparatus according to the present invention;

FIG. 8 is a cross-sectional view illustrating a fourth embodiment of theTN-mode LCD apparatus according to the present invention;

FIG. 9 is a cross-sectional view illustrating a fifth embodiment of theTN-mode LCD apparatus according to the present invention;

FIGS. 10, 11, 12, 13 and 14 are cross-sectional views illustratingmodifications of the apparatuses of FIGS. 4, 6, 7, 8 and 9,respectively;

FIG. 15 is a cross-sectional view illustrating a fifth embodiment of theTN-mode LCD apparatus according to the present invention;

FIG. 16 is a perspective view of the liquid crystal layer of FIG. 15;

FIG. 17 is a cross-sectional view illustrating a seventh embodiment ofthe TN-mode LCD apparatus according to the present invention;

FIGS. 18 and 19 are cross-sectional views illustrating modifications ofthe apparatuses of FIGS. 15 and 17, respectively;

FIG. 20 is a cross-sectional view illustrating an eighth embodiment ofthe TN-mode LCD apparatus according the present invention;

FIG. 21 is a cross-sectional view illustrating a ninth embodiment of theTN-mode LCD apparatus according to the present invention;

FIGS. 22 and 23 are cross-sectional views illustrating modifications ofthe apparatuses of FIGS. 20 and 21, respectively;

FIG. 24 is a perspective view for explaining the manufacturing steps ofthe transparent substrate and the transparent electrode of FIGS. 4, 7,10, 12, 15 and 18;

FIG. 25 is a photograph showing the state of liquid crystal moleculesformed on the transparent electrode of FIG. 24;

FIGS. 26A and 26B are perspective views for explaining the manufacturingsteps of the transparent substrate, the layer and the transparentelectrode of FIGS. 6, 8, 11, 13, 17 and 19;

FIG. 27 is a photograph showing the state of liquid crystal moleculesformed on the transparent electrode of FIG. 26B; and

FIGS. 28A and 28B are other perspective views for explaining themanufacturing steps of the transparent substrate, the layer and thetransparent electrode of FIGS. 6, 8, 11, 13, 17 and 19.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the description of the preferred embodiments, a prior art LCDapparatus will be explained with reference to FIGS. 1, 2 and 3.

In FIG. 1, which is a cross-sectional view illustrating a prior arttransmission-type TN-mode LCD apparatus, reference numeral 1 designatesa polarization plate for passing the frequency component of an incominglight X in a specified direction. Also, reference numeral 2 designates atransparent substrate on which a transparent electrode 3 made of indiumtin oxide (ITO) is coated. Similarly, reference numeral 4 designates apolarization plate for passing an outgoing light having a frequencycomponent in a specified direction. Also, reference numeral 5 designatesa transparent substrate on which a transparent electrode 6 made of ITOis coated. Further, a liquid crystal layer 7 is provided between thetransparent electrodes 3 and 6 with a gap d therebetween. In this case,the orientation of liquid crystal molecules in the liquid crystal layer7 is twisted.

The operation of the apparatus of FIG. 1 is explained below;

First, assume that no voltage is applied between the transparentelectrodes 3 and 6. The incident light X as well as natural light isconverted by the polarization plate 1 into a linearly polarized light.Then, this light penerates the transparent substrate 2 and thetransparent electrode 3, and is incident to the liquid crystal layer 7.In the liquid crystal layer 7, while the plane of polarization of theincident light is changed by the double refraction characteristics ofthe liquid crystal layer 7, the light reaches the transparent electrode6. Then, the light penerates the transparent electrode 6 and thetransparent substrate 5. As a result, only the frequency component oflight in the specified direction passes through the polarization plate4, thus obtaining an outgoing light Y1. This is called a first opticalstate.

Next, assume that a voltage is applied between the transparentelectrodes 3 and 6. In this case, the orientation of the liquid crystalmolecules in the liquid crystal layer 7 is changed due to the anistropicdielectric characteristics thereof in accordance with the electric fieldbetween the transparent electrodes 3 and 6. As a result, the plane ofpolarization of the light which has reached the transparent electrode 6is different from that where no voltage is applied between thetransparent electrodes 3 and 6. As a result, an outgoing light Y2different from the outgoing light Y1 is obtained. This is called asecond optical state.

Thus, an optical switching between the first optical state and thesecond optical state is possible depending on whether or not a voltageis applied between the transparent electrodes 3 and 6.

Generally, when the twisted angle of liquid crystal molecules is smallerthan a definite value around 270°, the tilt angle of liquid crystalmolecules has a linear relationship to the voltage applied between thetransparent electrodes 3 and 6. On the other hand, when the twistedangle of liquid crystal molecules is larger than the above-mentionedvalue, the tilt angle of liquid crystal molecules has an S-shapedrelationship to the voltage applied between the transparent electrodes 3and 6. Therefore, the transient orientation state of liquid crystalmolecules during a rising voltage is different from that during afalling voltage. As a result, when an intermediate voltage between ahigh voltage and a low voltage is applied between the transparentelectrodes 3 and 6, there are two orientation states of liquid crystalmolecules mixed within one pixel. This can be observed as an orientationdefect called a finger texture as shown in FIG. 2. Thus, a largehysteresis is generated in the voltage-to-light transmittancecharacteristics as shown in FIG. 3, so that a gray scale display isimpossible.

In order to realize a small hysteresis, an initial orientation operationsuch as a rubbing operation is not carried out, so that the orientationof crystal liquid molecules is in an amorphous state (see T. Sugiyama etal., “A Reflective a-N*GH-LCD and Its Ergonomic Characterization andOptimization”, SID 96 Digest, pp. 35-38, 1996). In this case, however,the orientation of liquid crystal molecules is easily caused by theinjection of liquid crystal into the space between the transparentelectrodes 3 and 6, and in addition, it is difficult to supervise thetemperature of liquid crystal during the injection thereof.

In FIG. 4, which illustrates a first embodiment of the presentinvention, the transparent substrate 5 and the transparent electrode 6of FIG. 1 are modified into a transparent substrate 5′ and a transparentelectrode 6′, respectively. That is, the surface of the transparentsubstrate 5′ is made uneven by using an etching process, a sand blastingprocess or a polishing process. Since the transparent electrode 6′ madeof ITO is formed on the uneven transparent substrate 5′ by anevaporation process,a sputtering process or a coating process, thesurface of the transparent electrode 6′ is made uneven. Also, thetwisted angle of liquid crystal molecules between the transparentelectrodes 3 and 6′ is about 270° to 450°

Also, in FIG. 4, the incident light X as well as natural light isconverted by the polarization plate 1 into a linearly polarized light.Then, this light penerates the transparent substrate 2 and thetransparent electrode 3 and is incident to the liquid crystal layer 7.In the liquid crystal layer 7, while the plane of polarization of theincident light is changed by the double refraction characteristics ofthe liquid crystal layer 7, the light reaches the transparent electrode6′. Then, the light penerates the transparent electrode 6′ and thetransparent substrate 5′. As a result, only the frequency component oflight in the specified direction passes through the polarization plate4, thus obtaining an outgoing light Y1 or Y2.

In the liquid crystal layer 7, a gap between the transparent electrodes3 and 6′ is changed from d1 to d2 within one pixel, so that an electricfield applied to the liquid crystal layer 7 is changed within one pixelin accordance with the gap. As a result, the electric field isfluctuated within one pixel, so that a threshold voltage and asaturation voltage of liquid crystal are changed microscopically withinone pixel. Therefore, although a large hysteresis is generatedmicroscopically within one pixel, in other words, a large number ofdifferent threshold voltages are generated microscopically within onepixel, the different threshold voltages are summed within one pixel, sothat the hysteresis of liquid crystal in the entire one pixel is madesmall as shown in FIG. 5. In addition, the transition curve of thevoltage-to-light transmittance characteristics is relatively sloped, sothat the gray scale display characteristics can be improved.

In FIG. 6, which illustrates a second embodiment of the presentinvention, a layer 8 having an uneven surface is formed on thetransparent substrate 5 of FIG. 1, and a transparent electrode 6′ madeof ITO is formed on the layer 8. Since the surface of the layer 8 isuneven, the surface of the transparent electrode 6′ is also uneven.Thus, in the same way as in the first embodiment, the hysteresis ofliquid crystal on the entire one pixel is made small, thus improving thegray scale display characteristics. Note that the layer 8 is made ofinorganic material or organic material such as polyimide or acrylicresin.

In FIG. 7, which illustrates a third embodiment of the presentinvention, a leveling layer 9 is buried in the recess portions of thetransparent electrode 6′ of FIG. 4. In this case, the leveling layer 9is made of organic or inorganic material having a permittivity equal toor smaller than that of the liquid crystal layer 7. Thus, the thicknessof the liquid crystal layer 7 is uniform regardless of the unevenness ofthe transparent electrode 6′, which suppresses the fluctuation of theorientation of liquid crystal molecules. This contributes to theimprovement of the display characteristics.

Also, in FIG. 7, at the recess portions of the transparent electrode 6′,the voltage applied between the transparent electrodes 3 and 6′ isdivided by the liquid crystal layer 7 and the leveling layer 9, thussubstantially reducing the voltage applied to the liquid crystal layer 7on the recess portions of the transparent electrode 6′. As a result, theelectric field is fluctuated within one pixel. Thus, in the same way asin the first embodiment, the hysteresis of liquid crystal on the entireone pixel is made small, thus improving the gray scale displaycharacteristics.

In FIG. 8, which illustrates a fourth embodiment of the presentinvention, a leveling layer 9 is buried in the recess portions of thetransparent electrode 6′ of FIG. 6. Also, in this case, the levelinglayer 9 is made of organic or inorganic material having a permittivityequal to or smaller than that of the liquid crystal layer 7. Thus, thethickness of the liquid crystal layer 7 is uniform regardless of theunevenness of the transparent electrode 6′, which suppresses thefluctuation of the orientation of liquid crystal molecules. Thiscontributes to the improvement of the display characteristics.

Also, in FIG. 8, at the recess portions of the transparent electrode 6′,the voltage applied between the transparent electrodes 3 and 6′ isdivided by the liquid crystal layer 7 and the leveling layer 9, thussubstantially reducing the voltage applied to the liquid crystal layer 7on the recess portions of the transparent electrode 6′. As a result, theelectric field is fluctuated within one pixel. Thus, in the same way asin the second embodiment, the hysteresis of liquid crystal on the entireone pixel is made small, thus improving the gray scale displaycharacteristics.

In FIG. 9, which illustrates a fifth embodiment of the presentinvention, a layer 8 having an uneven surface is formed on thetransparent electrode 6 of FIG. 1. In this case, the layer 8 is made oforganic or inorganic material having a permittivity equal to or smallerthan that of the liquid crystal layer 7. As the recess portions of thelayer 8, the voltage applied between the transparent electrodes 3 and 6per se is applied the liquid crystal layer 7. On the other hand, at theprotrusion portions of the layer, the voltage applied between thetransparent electrodes 3 and 6′ is divided by the liquid crystal layer 7and the layer 8, thus substantially reducing the voltage applied to theliquid crystal layer 7 on the protrusion portions of the layer 8. As aresult, the electric field is fluctuated within one pixel. Thus, in thesame way as in the first embodiment, the hysteresis of liquid crystal onthe entire one pixel is made small, thus improving the gray scaledisplay characteristics.

In FIGS. 10, 11, 12, 13 and 14, the apparatuses of FIGS. 4, 6, 7, 8 and9, respectively, are applied to reflection-type TN-mode LCD apparatuses,which do not require back lights. That is, a reflective electrode 10′ or10 made of aluminum or the like is provided instead of the transparentelectrode 6 or 6′ of FIGS. 4, 6, 7, 8 and 9. Also, a phase differencecompensation plate 11 is inserted between the polarization plate 1 andthe transparent substrate 2 of FIGS. 4, 6, 7, 8 and 9. Further, thepolarization plate 4 of FIGS. 4, 6, 7, 8 and 9 is not provided. Thetransparent substrate 5 or 5′ can be opaque, i.e., made of metal,polymer or ceramic.

Note that the reflective electrode 10 or 10′ can be formed by asputtering process.

In FIGS. 10, 11, 12, 13 and 14, an incident light X as well as naturallight is converted by the polarization plate 1 into a linearly polarizedlight. Then, this light penerates the phase difference compensationplate 11, the transparent substrate 2 and the transparent electrode 3,and is incident to the liquid crystal layer 7. In the liquid crystallayer 7, while the plane of polarization of the incident light ischanged by the double refraction characteristics of the liquid crystallayer 7, the light reaches the reflective electrode 10 or 10′.

On the other hand, light reflected from the reflective electrode 10 or10′ is again incident to the liquid crystal layer 7. In the liquidcrystal layer 7, while the plane of polarization of the incident lightis changed by the double refraction characteristics of the liquidcrystal layer 7, the light reaches the transparent electrode 3. Then,the light again penerates the transparent electrode 3, the transparentsubstrate 2 and the phase difference compensation plate 11. As a result,only the frequency component of light in a specified direction passesthrough the polarization plate 1, thus obtaining an outgoing light Y1 orY2.

In FIGS. 10, 11, 12, 13 and 14, in the same way as in the first, second,third, fourth and fifth embodiments, the hysteresis of liquid crystalmolecules is made small, thus improving the gray scale displaycharacteristics.

In FIG. 15, which illustrates a sixth embodiment of the presentinvention, oriented layers 12 and 13 are formed on the transparentelectrodes 3 and 6′, respectively, of FIG. 4. Rubbing processes areperformed on the oriented layers 12 and 13, to give an initialorientation to the liquid crystal layer 7. This suppresses thefluctuation of orientation of liquid crystal molecules caused by theinjection of liquid crystal between the transparent substrates 2 and 5′.

In addition, in FIG. 15, since the surface of the transparent substrate5′ is uneven, so that the surface of the oriented layer 13 is uneven,the pretilt angle of liquid crystal molecules is dependent upon theuneven surface of the oriented layer 13. For example, the pretilt angleof a domain D1 is indicated by θ₁, and the pretilt angle of a domain D4is indicated by θ₂. Therefore, there is discontinuity of the pretiltangle among the domains D1, D2, . . . , which are independent of eachother, as illustrated in FIG. 16, where reference M designates a liquidcrystal molecule. Since the threshold voltage and saturation voltage ofeach domain are also dependent upon the pretilt angle, there are manythreshold voltages and saturation voltages within one pixel. Therefore,although a large hysteresis is generated microscopically within onepixel, in other words, a large number of different threshold voltagesare generated microscopically within one pixel, the different thresholdvoltages are summed within one pixel, so that the hysteresis of liquidcrystal in the entire one pixel is also made small as shown in FIG. 5.In addition, the transition curve of the voltage-to-light transmittancecharacteristics is relatively sloped, so that the gray scale displaycharacteristics can be improved.

In FIG. 17, which illustrates a seventh embodiment of the presentinvention, in the same way as in the second embodiment, a layer 8 havingan uneven surface is formed on the transparent substrate 5 of FIG. 1,and a transparent electrode 6′ made of ITO is formed on the layer 8.Since the surface of the layer 8 is uneven, the surface of thetransparent electrode 6′ is also uneven. Thus, in the same way as in thesixth embodiment, the pretilt angle of liquid crystal molecules isdependent upon the uneven surface of the oriented layer 13. As a result,the hysteresis of liquid crystal on the entire one pixel is made small,thus improving the gray scale display characteristics.

In FIGS. 18 and 19, the apparatuses of FIGS. 15 and 17, respectively,are applied to reflection-type TN-mode LCD apparatuses, which do notrequire back lights. That is, a reflective electrode 10′ made ofaluminum or the like is provided instead of the transparent electrode 6′of FIGS. 15 and 17. Also, a phase difference compensation plate 11 isinserted between the polarization plate 1 and the transparent substrate2 of FIGS. 15 and 17. Further, the polarization plate 4 of FIGS. 15 and17 is not provided. The transparent substrate 5′ can be opaque, i.e.,made of metal, polymer or ceramic.

In FIGS. 18 and 19, an incident light X as well as natural light isconverted by the polarization plate 1 into a linearly polarized light.Then, this light penerates the phase difference compensation plate 11,the transparent substrate 2 and the transparent electrode 3, and isincident to the liquid crystal layer 7. In the liquid crystal layer 7,while the plane of polarization of the incident light is changed by thedouble refraction characteristics of the liquid crystal layer 7, thelight reaches the reflective electrode 10′.

On the other hand, light reflected from the reflective electrode 10′ isagain incident to the liquid crystal layer 7. In the liquid crystallayer 7, while the plane of polarization of the incident light ischanged by the double refraction characteristics of the liquid crystallayer 7, the light reaches the transparent electrode 3. Then, the lightagain penerates the transparent electrode 3, the transparent substrate 2and the phase difference compensation plate 11. As a result, only thefrequency component of light in a specified direction passes through thepolarization plate 1, thus obtaining an outgoing light Y1 or Y2.

In FIGS. 18 and 19, in the same way as in the sixth and seventhembodiments, the hysteresis of liquid crystal molecules is made small,thus improving the gray scale display characteristics.

In FIG. 20, which illustrates an eighth embodiment of the presentinvention, oriented layers 12 and 13 are formed on the transparentelectrodes 3 and 6, respectively, of FIG. 1. Rubbing processes areperformed on the oriented layers 12 and 13, to give an initialorientation to the liquid crystal layer 7. This suppresses thefluctuation of orientation of liquid crystal molecules caused by theinjection of liquid crystal between the transparent substrates 2 and 5.

In addition, in FIG. 20, the direction of a rubbing process performedupon a domain D1 of the oriented layer 13 is different from thedirection of a rubbing process performed upon a domain D2 of theoriented layer 13. As a result, the pretilt angle of liquid crystalmolecules is dependent upon the domains D1 and D2 of the oriented layer13. For example, the pretilt angle of the domain D1 is indicated by θ₁,and the pretilt angle of the domain D2 is indicated by θ₂. Therefore,there is discontinuity of the pretilt angle between the domains D1 andD2, which are independent of each other. Since the threshold voltage andsaturation voltage of each domain are also dependent upon the pretiltangle, there are two threshold voltages arid two saturation voltageswithin one pixel. Therefore, although a large hysteresis is generatedwithin each domain of one pixel, in other words, two different thresholdvoltages are generated microscopically within one pixel, the twodifferent threshold voltages are summed within one pixel, so that thehysteresis of liquid crystal in the entire one pixel is also made smallas shown in FIG. 5. In addition, the transition curve of thevoltage-to-light transmittance characteristics is relatively sloped, sothat the gray scale display characteristics can be improved.

In FIG. 21, which illustrates a ninth embodiment of the presentinvention, oriented layers 12 and 13 are formed on the transparentelectrodes 3 and 6, respectively, of FIG. 1. Rubbing processes areperformed on the oriented layers 12 and 13, to give an initialorientation to the liquid crystal layer 7. This suppresses thefluctuation of orientation of liquid crystal molecules caused by theinjection of liquid crystal between the transparent substrates 2 and 5.

In addition, in FIG. 21, the tilt angle of liquid crystal molecules isdifferent in domains D1 and D2 by dispersing polymer into the liquidcrystal layer 7. That is, about 0.1 to 5 weight percent of monomer andoligomer are mixed in liquid crystal before the injection of liquidcrystal between the oriented layers 12 and 13. In this case, the monomeris converted by ultraviolet irradiation or heat into polymer, and theoligomer serves as an initiator for this polymerization. After theinjection, the liquid crystal is heated so that the liquid crystalenters a liquid phase. Then, the liquid crystal is cooled while anelectric field or a magnetic field is applied thereto. At a specifiedtemperature during this cooling operation, the liquid crystal issubjected to ultraviolet or the like, so that the monomer is convertedinto a polymer network as indicated by N. Since the polymerization iscarried out under an electric field or a magnetic field, the polymernetwork is arranged in accordance with the tilt angle of liquid crystalmolecules. Therefore, even when the electric field applied between thetransparent electrodes 3 and 6 is 0, the tilt angle of liquid crystalmolecules is different in domains D1 and D2 within the bulk of theliquid crystal layer 7. As a result, when a voltage is applied betweenthe transparent electrodes 3 and 6, the pretilt angle of liquid crystalmolecules is dependent upon the domains D1 and D2 of the oriented layer13. For example, the pretilt angle of the domain D1 is indicated by θ₁,and the pretilt angle of the domain D2 is indicated by θ₂. Therefore,there is discontinuity of the pretilt angle between the domains D1 andD2, which are independent of each other. Since the threshold voltage andsaturation voltage of each domain are also dependent upon the pretiltangle, there are two threshold voltages and two saturation voltageswithin one pixel. Therefore, although a large hysteresis is generatedwithin each domain of one pixel, in other words, two different thresholdvoltages are generated microscopically within one pixel, the twodifferent threshold voltages are summed within one pixel, so that thehysteresis of liquid crystal in the entire one pixel is also made smallas shown in FIG. 5. In addition, the transition curve of thevoltage-to-light transmittance characteristics is relatively sloped, sothat the gray scale display characteristics can be improved.

In FIGS. 22 and 23, the apparatuses of FIGS. 20 and 21, respectively,are applied to reflection-type TN-mode LCD apparatuses, which do notrequire back lights. That is, a reflective electrode 10 made of aluminumor the like is provided instead of the transparent electrode 6 of FIGS.20 and 21. Also, a phase difference compensation plate 11 is insertedbetween the polarization plate 1 and the transparent substrate 2 ofFIGS. 20 and 21. Further, the polarization plate 4 of FIGS. 20 and 21 isnot provided. The transparent substrate 5 can be opaque, i.e., made ofmetal, polymer or ceramic.

In FIGS. 22 and 23, an incident light X as well as natural light isconverted by the polarization plate 1 into a linearly polarized light.Then, this light penerates the phase difference compensation plate 11,the transparent substrate 2 and the transparent electrode 3, and isincident to the liquid crystal layer 7. In the liquid crystal layer 7,while the plane of polarization of the incident light is changed by thedouble refraction characteristics of the liquid crystal layer 7, thelight reaches the reflective electrode 10.

On the other hand, light reflected from the reflective electrode 10 isagain incident to the liquid crystal layer 7. In the liquid crystallayer 7, while the plane of polarization of the incident light ischanged by the double refraction characteristics of the liquid crystallayer 7, the light reaches the transparent electrode 3. Then, the lightagain penerates the transparent electrode 3, the transparent substrate 2and the phase difference compensation plate 11. As a result, only thefrequency component of light in a specified direction passes through thepolarization plate 1, thus obtaining an outgoing light Y1 or Y2.

In FIGS. 22 and 23, in the same way as in the eighth and ninthembodiments, the hysteresis of liquid crystal molecules is made small,thus improving the gray scale display characteristics.

The manufacturing steps of the transparent substrate 5′ and thetransparent electrode 6′ of FIGS. 4, 7, 10, 12, 15 and 18 will beexplained next with reference to FIGS. 24 and 25. First, a planetransparent substrate is polished by using a #1000 abrasive material,and then, is etched by 25 percent fluoric acid for about 3 minutes. As aresult, a randomly uneven surface is formed on the transparent substrate5′. Also, ITO is formed on the transparent substrate 5′, thus obtainingthe transparent electrode 6′. In this case, the depths of recessportions of the transparent electrode 6′ are randomly changed within onepixel. Also, protrusion portions of the transparent electrode 6′ areseparated from each other by the recess portions thereof. A liquidcrystal layer on the transparent electrode 6′ was observed as shown inFIG. 25. In FIG. 25, white portions indicate ON state domains of liquidcrystal molecules, and black portions indicate OFF state domains ofliquid crystal molecules. Therefore, orientation defects are notgenerated, and ON state domains and OFF state domains are completelymixed, thus improving the gray scale display characteristics.

A first example of the manufacturing steps of the transparent substrate5, the layer 8 and the transparent electrode 6′ of FIGS. 6, 8, 11, 13,17 and 19 will be explained next with reference to FIGS. 26A, 26B and27.

First, as illustrated in FIG. 26A, a plurality of pillar base elements81 are randomly formed on a plane transparent substrate 5 within onepixel. In this case, note that the locations of the base elements 81 arerandomly changed, and also, the heights of the base elements 81 arerandomly changed.

Next, as illustrated in FIG. 26B, an insulating layer 82 made ofinorganic material or organic material such as polyimide or acrylicresin is formed on the transparent substrate 5. In this case, due to thepillar base elements 81, the surface of the insulating layer 82 is madeuneven. Thus, the pillar base elements 81 and the insulating layer 82form the uneven layer 8. Then, an ITO layer is coated on the uneveninsulating layer 82 to form the transparent electrode 6′. The surface ofthe transparent electrode 6′ is uneven due to the uneven surface of theinsulating layer 82. In this case, protrusion portions are separatedfrom each other by recess portions. A liquid crystal layer on thetransparent electrode 6′ was observed as shown in FIG. 27. In FIG. 27,white portions indicate ON state domains of liquid crystal molecules,and black portions indicate OFF state domains of liquid crystalmolecules. Therefore, finger texture type orientation defects are hardlygenerated, and ON state domains and OFF state domains are mixed, thusimproving the gray scale display characteristics.

A second example of the manufacturing steps of the transparent substrate5, the layer 8 and the transparent electrode 6′ of FIGS. 6, 8, 11, 13,17 and 19 will be explained with reference to FIGS. 28A and 28B.

First, as illustrated in FIG. 28A, a base element 81′ is formed on aplane transparent substrate 5. Then, the base element 81′ is etched by aphotolithography and etching process, so that a plurality of holes 81′ aare perforated in the base element 81′ within one pixel. In this case,the sizes of the holes 81′ a are randomly changed within one pixel.

Next, as illustrated in FIG. 28B, an insulating layer 82 made ofinorganic material or organic material such as polyimide or acrylicresin is formed on the transparent substrate 5. In this case, due to thebase element 81′, the surface of the insulating layer 82 is made uneven.Thus, the base elements 81′ and the insulating layer 82 form the unevenlayer 8. Then, an ITO layer is coated on the uneven insulating layer 82to form the transparent electrode 6′. The surface of the transparentelectrode 6′ is uneven due to the uneven surface of the insulating layer82. In this case, since the sizes of the holes 81′a are randomly changedwithin one pixel, the depths of recess portions of the transparentelectrode 6′ are randomly changed within one pixel. Also, recessportions are separated from each other by the protrusion portions. Evenin this case, in a liquid crystal layer on the transparent electrode 6′,finger texture type orientation defects are hardly generated, and ONstate domains and OFF state domains are mixed, thus improving the grayscale display characteristics.

In the above-described embodiments, when color filters are combined withthe apparatus, a full color LCD apparatus can be realized.

Also, in the above-described embodiments, when two-tone dye is mixedinto the liquid crystal of the liquid crystal layer 7, a guest host typeLCD apparatus can be realized.

As explained hereinabove, according to the present invention, thehysteresis of the voltage-to-light transmittance of the liquid crystallayer can be made small, to improve the gray scale displaycharacteristics.

What is claimed is:
 1. An active type liquid crystal display apparatuscomprising: first and second polarization plates; first and second planetransparent substrates between said first and second polarizationplates; a layer having a randomly uneven surface and being formed on aninner surface of said second plane transparent substrate; a firsttransparent electrode formed on an inner surface of said firsttransparent substrate; a second transparent electrode formed on saidlayer; and a twisted-mode type liquid crystal layer provided betweensaid first and second transparent electrodes, wherein a twisted angle ofliquid crystal molecules in said twisted-mode type liquid crystal layerbeing between about 270° and 450°, and pretilt angles of liquid crystalmolecules in the liquid crystal layer are fluctuated within one pixel.2. An active type liquid crystal display apparatus comprising: firstarid second polarization plates; first and second plane transparentsubstrates between said first and second polarization plates; a layerhaving a randomly uneven surface and being formed on an inner surface ofsaid second plane transparent substrate; a first transparent electrodeformed on an inner surface of said first transparent substrate; a secondtransparent electrode formed on said layer; a leveling layer buried inrecess portions of said second transparent electrode; and a twisted-modetype liquid crystal layer provided between said first transparentelectrode and said leveling layer, wherein said leveling layer has apermittivity not larger than a permittivity of said liquid crystallayer, a twisted angle of liquid crystal molecules in said twisted-modetype liquid crystal layer being between about 270° and 450°, and pretiltangles of liquid crystal molecules in the liquid crystal layer arefluctuated within one pixel.
 3. An active type liquid crystal displayapparatus comprising: first and second polarization plates; first andsecond plane transparent substrates between said first and secondpolarization plates; first and second plane transparent electrodesbetween said first and second plane transparent substrates; a layerhaving a randomly uneven surface and being formed on an inner surface ofsaid second plane transparent electrode; and a twisted-mode type liquidcrystal layer provided between said first transparent electrode and saidlayer, wherein said layer has a permittivity not larger than apermittivity of said liquid crystal layer, a twisted angle of liquidcrystal molecules in said twisted-mode type liquid crystal layer beingbetween about 270° and 450°, and pretilt angles of liquid crystalmolecules in the liquid crystal layer are fluctuated within one pixel.4. An active type liquid crystal display apparatus comprising: apolarization plate; a phase difference compensation layer provided on aninner side of said polarization plate; first and second plane substratesprovided on an inner side of said phase difference compensation layer,said first plane substrate being transparent; a layer having a randomlyuneven surface and being formed on an inner surface of said second planesubstrate; a first electrode formed on an inner surface of said firstsubstrate, said first electrode being transparent; a second electrode ofa reflection type formed on said layer; and a twisted-mode type liquidcrystal layer provided between said first and second electrodes, whereina twisted angle of liquid crystal molecules in said twisted-mode typeliquid crystal layer being between about 270° and 450°, wherein athickness of said liquid crystal layer varies within a single pixel, andpretilt angles of liquid crystal molecules in the liquid crystal layerare fluctuated within one pixel.
 5. An active type liquid crystaldisplay apparatus comprising: a polarization plate; a phase differencecompensation layer provided on an inner side of said polarization plate;first and second plane substrates, wherein said first substrate isprovided on an inner side of said phase difference compensation layer,said first plane substrate being transparent; a layer having a randomlyuneven surface and being formed on an inner surface of said second planesubstrate; a first electrode formed on an inner surface of said firstsubstrate, said first electrode being transparent; a second electrode ofa reflection type formed on said layer; a leveling layer buried inrecess portions of said second electrode; and a twisted-mode type liquidcrystal layer provided between said first electrode and said levelinglayer, wherein said leveling layer has a permittivity not larger than apermittivity of said liquid crystal layer, a twisted angle of liquidcrystal molecules in said twisted-mode type liquid crystal layer beingbetween about 270° and 450°, wherein a thickness of said liquid crystallayer varies within a single pixel, and pretilt angles of liquid crystalmolecules in the liquid crystal layer are fluctuated within one pixel.6. An active type liquid crystal display apparatus comprising: apolarization plate; a phase difference compensation layer provided on aninner side of said polarization plate; first and second plane substratesprovided on an inner side of said phase difference compensation layer,said first plane substrate being transparent; first and second planeelectrodes between said first and second plane substrates, said firstplane electrode being transparent, said second plane electrode being ofa reflection type; a layer having a randomly uneven surface and beingformed on an inner surface of said second plane electrode; and atwisted-mode type liquid crystal layer provided between said firstelectrode and said said layer has a permittivity not larger than apermittivity of said liquid crystal layer, a twisted angle of liquidcrystal molecules in said twisted-mode type liquid crystal layer beingbetween about 270° and 450°, wherein a thickness of said liquid crystallayer varies within a single pixel, and pretilt angles of liquid crystalmolecules in the liquid crystal layer are fluctuated within one pixel.7. An active type liquid crystal display apparatus comprising: first andsecond polarization plates; first and second plane transparentsubstrates between said first and second polarization plates; a layerhaving a randomly uneven surface and being formed on an inner surface ofsaid second plane transparent substrate; a first transparent electrodeformed on an inner surface of said first transparent substrate; a secondtransparent electrode formed on said layer; first and second orientedlayers formed on inner surfaces of said first and second transparentelectrodes, respectively, wherein said second oriented layer has anuneven inner surface; and a twisted-mode type liquid crystal layerprovided between said first and second oriented layers, wherein saidsecond oriented layer causes said liquid crystal layer to form aplurality of domains wherein there is discontinuity of the pretilt angleamong individual domains whereupon pretilt angles of liquid crystalmolecules in the liquid crystal layer are fluctuated within one pixel.8. An active type liquid crystal display apparatus comprising: apolarization plate; a phase difference compensation layer provided on aninner side of said polarization plate; first and second plane substratesprovided on an inner side of said phase difference compensation layer,said first plane substrate being transparent, a layer having a randomlyuneven surface and being formed on an inner surface of said second planesubstrate; a first electrode formed on an inner surface of said firstsubstrate, said first electrode being transparent; a second electrode ofa reflection type formed on said layer; first and second oriented layersformed on inner surfaces of said first and second electrodes,respectively, wherein said second oriented layer has an uneven-innersurface; and a twisted-mode type liquid crystal layer provided betweensaid first and second oriented layers, wherein said second orientedlayer causes said liquid crystal layer to form a plurality of domainswherein there is discontinuity of the pretilt angle among individualdomains whereupon pretilt angles of liquid crystal molecules in theliquid crystal layer are fluctuated within one pixel.